The present invention relates to controlling power levels of optical signals, and more particularly to controlling power levels of optical signals in optical fibers.
Optical fibers are often used in conjunction with high power lasers, such as for laser welding and cutting, or medical applications, and the art has developed approaches for enhancing the safety of these systems. For example, U.S. Pat. No. 4,449,043 to Husbands discloses a safety device for a high power fiber optic system, which may present a hazard when an optical connector is unmated. The safety device includes a four-port optical coupler which transmits, to a receiver, a portion of the output power, as well as backscattered energy, which is developed between the glass-to-air and air-to-glass interfaces between adjacent connectors. A comparison between the output power and the backscattered energy is used to disable the laser source when an unmated condition is detected.
U.S. Pat. No. 4,543,477 to Doi et al. discloses a safety device for a medical laser wherein reflected laser light is detected from the exit end surface of a fiber and a shutter is used to stop the laser if a breakage of the fiber is detected. Ortiz Jr., in U.S. Pat. No. 4,812,641, discloses a high power laser for material processing and includes respective photodetectors to sense the laser power exiting a power optical fiber and the laser injection power. The two power levels are compared to detect whether a break in the power transmitting fiber has occurred. U.S. Pat. No. 4,673,795, also to Ortiz Jr., discloses an interlock safety arrangement which includes an optical sensor connected to the controller for turning the laser off when the laser beam has turned on but laser energy does not reach a remote module, indicating a break in the high power transmitting optical fiber.
The described prior art discloses that the power levels before and after the optical fiber are measured and compared. Such an approach leads to disadvantages of complexity at the output end of a fiber and, therefore, additional cost of fabrication and difficulty of operation. Such an approach also causes a loss of optical energy that would have otherwise been delivered to a receiver at output end of the fiber.
The present invention presents an approach for transmitting high power optical signals through fibers while helping keep the operation safe under regulatory requirements. In the inventive approach, a breakage in the fiber causing a leak of the optical signal outside the fiber is detected and the source of the optical signal is caused to lower the power of the optical signal being fed into the fiber. In the inventive approach, inherently risky power levels generated by the source of optical signals are detected and the source is caused to lower the power of the optical signal.
The inventive approach keeps simple the output end of the fiber transmitting the optical signal and, therefore, lowers the fabrication cost and simplifies operation. It also does not obtain information from the input end of the fiber and therefore conserves the optical energy for transmission into the fiber. Moreover, because of its simpler arrangement, the inventive approach has higher reliability in determining whether the optical fiber is broken.
The present invention achieves the above mentioned advantages by using a fiber optical interconnection structure that at least has an optical fiber, a transmitter arranged to transmit an optical signal into a first end of the optical fiber, and a controller arranged to control the transmitter based on the power of the optical signal coming out of the other end of the fiber. However, the controller does not get information from the transmitter about the power of the optical signal being transmitted to the first end of the fiber. Rather, the controller gets information about the power of the optical signal coining out of the fiber. In an embodiment, the controller causes the transmitter to lower the power input into the optical fiber if the power coming out of the fiber is below an expected threshold amount. This protects the environment from optical signals leaking out of broken fibers and potentially harming individuals. In another embodiment, the controller causes the transmitter to lower the power input into the optical fiber if the power coming out of the fiber is above an expected threshold amount. This protects the system by preventing a runaway situation wherein the optical signal source uncontrollably increases the generated power of the optical signal. Of course the two embodiments may be used together in one system.